Quenching Studies of Hydrophobically-Modified Poly(N-isopropylacrylamides)

Fluorescence quenching by nitromethane of pyrene-labeled poly(N-isopropylacrylamides) (PNIPAMs) which contain alkyl chains was employed to investigate the accessibility of the quencher to the pyrene moieties. The quenching efficiency for monomeric pyrene or excimers was decreased in PNIPAMs when compared to the quenching efficiency of pyrene fluorescence in the aqueous phase, showing that pyrene is always located within the polymeric micelles. The contribution of static quenching was evaluated by comparing the quenching efficiency determined from steady-state measurements with that obtained from time-resolved data. Static quenching was present for all PNIPAMs studied. The decrease of the quenching efficiency was related to the polymeric micelle structure. The highest degree of protection was observed for the excimer emission of the polymer containing randomly-substituted alkyl chains and with the pyrene bound to the same polymeric unit as the alkyl chain.